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Expect Fukushima's Radioactive Ocean Plume to Hit the US Next Year

There will be a “measurable increase in radioactive materials,” but the concentration will be well below safety levels by that point.
Pacifica, CA via Franco Felini/Flickr

Within days of the 2011 Fukushima nuclear plant disaster, radiation could be detected in the atmosphere all the way from the America’s West Coast. But the plume of radionuclides, including Cesium-137, that was released into the Pacific Ocean is still spreading and dispersing, and will likely reach Hawaii and the northwestern American coastline next year.

The good news—the silver lining to the plume—is that even though there will be a “measurable increase in radioactive materials,” the concentration of those materials will be well below World Health Organization safety levels by that point.

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Projections from the paper show the concentration of Cesium-137 in the top 200 meters of the Pacific as it moves east. Figure A is for April 2012, B is April 2014, C is April 2016, and D is April 2021.

That's according to a study from the Centre of Excellence for Climate System Science, a mostly Australian research organization, which mapped the radioactive plume’s path through the world’s ocean for the next ten years. According to the report, “two energetic currents off the Japanese coast—the Kuroshio Current and the Kurushio Extension—are primarily responsible for accelerating the dilution of the radioactive material, taking it well below WHO safety levels within four months [of the incident].” Other eddies and whirlpools will continue the dilution process and direct the radioactive particles disparately westward, the study states.

While some traces of radiation will be found in the Indian and South Pacific Oceans, the radiation seems limited to the North Pacific for the first decade, before sinking into the deep ocean and spreading. Thanks to ocean currents, the plume will hit Oregon and northward first, and California a few years later, starting in 2016.

Map of ocean currents in the North Pacific via Wikimedia Commons.

Cs-137 has a half-life of over 30 years, so when it enters the environment—from Fukushima, from Chernobyl, from nuclear weapons tests in the 50s and 60s—it’s in for the long haul. There’s enough residual radiation in the air from nuclear testing that scientists can measure it in elephant tusks, and will be able to do so for at least another decade and a half—and the ban on above-ground nuclear tests was signed 50 years ago.

Under the best of circumstances, the radiation in the ocean from Fukushima will be evident for at least three decades. Recent reports suggest that these are far from the best circumstances, and if there’s any incentive to hurry to find a solution, it might be that a short-term problem has no short-term solution.